1. Field Of The Invention
The invention relates to a control system for operating a delayed coker apparatus in the process of converting a heavy liquid hydrocarbon feedstock to gaseous products, distillate liquid products and a solid coke product.
2. Description Of Relevant Methods In The Field
The delayed coking process is well-known in the petroleum refining arts for thermally decomposing a heavy liquid hydrocarbon to a solid coke product. The process is used primarily as a means of disposing of low value vacuum resids which are a minor fraction of full boiling range petroleum. The preferred products are hydrocarbon gas and distillate liquids. The resulting coke is a low value by-product. The value of this by-product is calculated based on the fuel value of the coke and the sulfur and heavy metal impurities which are transferred from the heavy hydrocarbon feedstock to the coke.
In the delayed coking process a feedstock such as a heavy, sour vacuum resid containing heavy metals is introduced to the bottom portion of a coker fractionator. The fractionator bottoms is then passed through a furnace to heat the bottoms to coking temperature and then to one of two coke drums. The hot hydrocarbon is retained in the coke drum at a temperature and pressure for a period of time to convert the liquid hydrocarbon to coke.
The two coke drums are operated cyclically. While one drum is being filled and coked, the other drum is emptied and readied for another filling. The coke emptying portion of the cycle involves steaming the coke with medium pressure steam to remove volatile hydrocarbon liquids and gases. Then the coke is cooled with quench water. The cooled coke is next hydraulically cut with high pressure water. The cut coke is removed from the coke drum to a coke pit and coke dewatering pad. Finally, the coke drum is heated with vapor from the other coke drum. The hydrocarbon and steam effluent from the heating coke drum is removed to a closed blowdown system. When the coke drum effluent reaches 350.degree. F. it is switched to the coker fractionator for hydrocarbon recovery.
U.S. Pat. No. 4,455,219 to H. R. Janssen et al. issued June 19, 1984 describes a delayed coking process which is typical of the commercial refining industry. This patent teaches the essential process parameters of the delayed coking process and is incorporated herein by reference.